Fog reduction in photographic silver halide emulsions



United States Patent FOG REDUCTION IN PHOTOGRAPHIC SILVE HALIDEEMULSIONS Fritz H; Dersch, Binghamton, N.Y., assignor to General Aniline& Film Corporation, New York, N.Y., a corporation of Delaware NoDrawing. Application May 27, 1958 Serial No. 738,047

Claims. (CI. 96-66) The present invention relates to the use ofantifogging and stabilizing agents for photographic silver halideemulsions and, more particularly, to the employment of his-(s-triazolopyrimidine) disulfides for such purpose.

It is recognized that light sensitive emulsions such as gelatino silverhalide emulsions have a tendency to fog. The fog may be causedin anumber of ways as, for example, by excessive ripening of the emulsion,by storage of the light sensitive element at elevated temperatures andhumidity or by prolonged development of the exposed emulsion.

. A great number of antifogging and stabilizing, agents have beenrecommended in the literature for the purpose of preventing theformation of fog in light sensitive silver halide emulsions. Althoughthese compounds have the ability to control fog during manufacture, aswell as during storage, they also have distinct shortcomings. Forinstance, they lower the sensitivity of the emulsion either immediatelyor under storage conditions, thus causing speed regression.

I have now found that the bis-(s-thiazolo [4,3-a] pyrimidine) disulfidesare excellent stabilizers and antifoggants for silver halide emulsionshaving the ability to maintain the sensitivity and fog at, or close to,initial optimum values under keeping conditions of high temperature andhumidity.

The use of such compounds to inhibit fog and to stabilize silver halideemulsions either by location of the same in the emulsion, in layersadjacent to the emulsion or in processing baths for the emulsion,constitutes the purposes and objects of the present invention.

The bis-(s-triazolo[4,3-a]pyrimidine)disulfides, the use of which iscontemplated herein, may be represented by the following formulae:

wherein R is hydrogen, alkyl, e.g., methyl, ethyl, propyl, isopropyl,butyl, amyl and the like; alicyclic, e.g., cyclopentyl, cyclohexyl andthe like; aryl, e.g., phenyl, naphthyl, diphenyl and the like; or aheterocyclic radical, e.g., pyridyl, furyl, pyrryl, pyrazolyl and R isamino, hydroxy, carbalkoxy, e.g., carbethoxy',carbopropoxy and thelike;or an alkyl, alic'yclic, 'aryl orheterocyclic radical of the same valueas R; and R and R together rep resent the atoms necessary to complete aS-membered or 6-membered alicyclic or heterocyclic ring structure, e.g.,cyclopentyl, cyclohexyl and the like; aryl e.g., phenyl, naphthyl,diphenyl; pyridyl, furyl, pyrryl, pyrazolyl and the like. R is hydrogenor a carbalkoxy group e.g., carbomethoxy, carbethoxy, carbopropoxy groupand R is either hydrogen, methyl or phenyl and X is an amino or hydroxygroup.

The general formula assigned to these products is based on the findingsof E. J. Birr and W. Walther published in Chemische Berichte, volume 86,pages 140l3 (1953). However, it is to be understood that the compoundsemployed in the present invention are compounds obtained by theprocesses outlined below, whatever their chemical structure mayultimately prove to be. Examples of compounds falling within the ambitof such general formula which we have found to be eifective are:

bis-(4 hydroxy 6 methyl s triazolo [4,3 a] pyrimidine)disulfide bis (4-hydroxy 6 phenyl s triazolo[4,3 alpyrimidine)disulfide bis (4 6dihydroxy s triazolo[4,3 alpyrimidine) disulfide 1,

bis (4 hydroxy 6 amino s triazolo[4,3 alpyrimidine)sulfide bis (4hydroxy 6 carbethoxy-s -triazolo[4,3 -a] pyrimidine) disulfide bis- (4hydroxy-6413 pyridyl)-s-triazoloi4,3 a)pyrimidine) disulfide bis(4hydroxy 6 cyclohexyl s triazolo[4,3 alpyrimidine)disulfide bis(4 hydroxy5 cyclohexyl 6 methyl s triazolo [4,3-a] pyrimidine)disulfide bis(4hydroxy 5 (a furyl) 6 Amethyl s triazolo [4,3-alpyrimidine) disulfidebis(4 hydroxy 5 phenyl 6 methyl s triazolo [4,3-a] pyrimidine) disulfidebis(4 hydroxy 6 (a furyl) s triazolo[4,3-alpyrim idine)disulfide bis(4hydroxy 6 benzyl s triazolo[4,3 alpyrimidine)disulfide bis(4 amino 6cyclohexyl s triazolot ifl alpyriljriidine) disulfide bis(4 amino Scyclohexyl 6 methyl s triazolo [4,3-a] pyrimidine) disulfide bis(4hydroxy 5,6 cyclopentano s triazol[4,3-a]

pyrimidine) disulfide bis(4 amino 5,6 cyclohexano s triazolo[4,3-a]

. pyrimidine)disulfide The above compounds are best prepared byoxidizing 'the 3-mercapto-s-triazolo[4,3-a]pyrimidine derivative inaqueous solution and in a mildly alkaline medium (pH=8.0-9.0) with amild oxidizing agent such as hydrogen peroxide or sodium or potassiumpersulfate. The S-mercapto-s-triazolo pyrimidines are prepared byreacting 5-amino-3-mercapto-4,1,2-triazole with a fi-keto ester, amalonic ester or a nitrile of a malonic ester as illustrated by UnitedStates Patent 2,444,605; with a B-immonitrile or a fl-ketonitrile asillustrated by United States Patent 2,444,606; with a cyclic fi-ketoester or a cyclic fi-ketonitrile as illustrated by United States Patent2,444,607; or with an alkoxymethylene malonic acid ester as illustratedby United States Patent 2,450,397. In general, the 2-mercapto-s-triazolo[4,3-alpyrimidine is obtained by heating themercapto-amino-triazole with the ester or nitrile in glacial acetic acidunder reflux conditions as described in the foregoing patents. In someinstances, the reaction can be carried out in the absence of the solventby employing somewhat higher temperatures than those required when asolvent is used.

Beneficial effects and fog reduction are obtained when aqueous oralcoholic solutions of the aforementioned compounds are incorporated inthe silver halide emulsions as ripening finals or as coating finals.

Ripening finals are added during the ripening or the sensitivityincreasing stage of the emulsion making process. Such additions may bemade before, during or after the decomposition of the soluble silversalt such as silver nitrate by means of a soluble halide such aspotassium bromide, sodium chloride or the like in the presence of acolloidal carrier such as gelatin, PVA, solubilized casein or albumen.

Coating finals are added to the emulsion just prior to coating on asuitable support such as glass, paper or film at a time when theemulsion has nearly obtained its maximum sensitivity.

When used as ripening finals, the antifoggants are best employed in aconcentration of 0.4 to 6.5 milligrams per mol of silver'halide and whenused as coating finals in a concentration 6 to 50 milligrams per mol ofsilver halide. The concentration used depends on the type of emulsionemployed and it is advisable to determine the optimum concentration fromcase to case. In some instances, it is advantageous to apply theantifoggant and stabilizers in layers adjacent to the emulsion, that is,in a separate undercoating layer or in the anti-abrasion gelatinsurface.

Grams Metol(p-methylaminophenol sulfate) 1.5 Sodium sulfite, anhydrous45 Sodium bisulfite 1 Hydroquinone 3 Sodium carbonate, monohydrated 6'Potassium bromide 0.8 Water to make 1 liter.

Speed (6 days at Quantity of Compound Relative Fog at after 50C.)0venadded Speed 12' Develoven fog at 6' opment test Development in otherinstances, the desired result may be obtained 15 by addition of theantifoggant and stabilizer to one of several processing baths such asdeveloper, fixer or the like.

The aforesaid antifoggants and stabilizers may be utilized in connectionwith any type of photographic emulsion, e.g., non-sensitized,orthochromatic, panchromatic, boiltype emulsions, color emulsions or thelike. They may be employed in combination with other known antifoggantsand stabilizers, reductionand metaland noble metal sensitizers, or incombination with hydroxypolyethenoxy derivatives, i.e., those obtainedby reacting ethylene oxide with an alcohol, phenol, amine or the like(see U.S.P. 1,970,578).

The mereaptotriazolopyrimidines from which my stabilizers are preparedhave previously been recommended as emulsion additives. However, thesemercaptotriazolopyrimidines have the inherent disadvantage of many othermercapto type stabilizers: They reduce fog at the sacrifice of speed andcontrast. These losses do not stop with the manufacturing operation, butprogress during the storage of the light-sensitive material, thusreducing the shelflife of the commercial product. The compounds of myinvention are free from these disadvantages.

The invention is illustrated by the following examples, but it is to beunderstood that the invention is not restricted thereto.

Example I A silver halide emulsion in gelatin containing 4 percentsilver iodide and 96 percent silver bromide was prepared in aconventional manner and brought up to its maximum light sensitivity. Itwas then readied for coating and finals were added such as sensitizingdyes, stabilizers and hardening agents. A 1 percent solution of bis-3(4-hydroxy 6 methyl s triazolo[4,3 a]pyrimidine)- disulfide was added tothe emulsion as an antifoggant. The emulsion samples weighed onekilogram and con- 'tained about 0.4 mol of silver halide. The soprepared emulsion samples were coated on a suitable cellulose ester baseand dried. Samples of these film coatings were then exposed in a TypeIIB Sensitometer and developed in a developer having the followingcomposition:

The bis 3(4 hydroxy 6 methyl s triazolo[4,3 a]- pyrimidine) disulfidewas prepared as follows:

Four grams of 5 amino 3 mercapto 4,1,2 triazole (Berichte, volume 54,page 2099) and 10 milliliters of ethyl acetoacetate were heated in 60milliliters of glacial acetic acid under reflux for 9 hours. The3-mercapto- 4 hydroxy 6 methyl s triazolo [4,3 a] pyrimidineprecipitated on cooling. The product melted at 281 C. afterrecrystallization.

Four grams of the mercapto compound were dissolved in 60 milliliters ofwater which had been made slightly alkaline by the addition of 1.0 gramof sodium hydroxide. A solution of potassium persulfate (K S O inmilliliters of water was added drop-wise during 25 minutes. Thetemperature rose to 27 C. at the start. The yellowish-white precipitatewhich was formed was filtered (yield Example 11 The procedure was thesame as in Example I except that thebis-3(-4-hydroxy-6-methyl-s-triazolo [4,3-a1pyrimidine)disulfide wasreplaced by an equivalent quantity of bis-3(-4-amino-6-methyl-s-triazole [4,3-a] pyrimidine) disulfide. The resultswere similar to these of Example I. This compound was prepared byreacting 1 mol of amino-3-mercapto-4,1,2-triazole with 1 mol ofacetoacetonitrile in boiling glacial acetic acid. The resultantmercaptotriazolopyrimidine was then oxidized with potassium persulfateas described in Example I.

Example I A solution containing 30 grams of gelatin and 100 mg. ofbis(4-hydroxy-6-methyl-s-triazole[4,3-a]pyrimidine)- disulfide per literof water was coated on a subbed filmbase in a manner known to the art.After coating was performed, a silver halide emulsion in gelatincontaining 4 percent silver iodide and 96 percent of silver bromide wascoated on top of the previously applied gelatin layer. After drying,film samples were exposed and processed as described in Example I. Thesamples exhibited a relative speed of 100 and a fog of 0.12 comparedwith a type coating of the same emulsion having an undercoating similarto that described above, but lacking the antifoggant and having a speedof 100 and a fog of 0.20.

Example V The procedure was the same as in Example IV excepting that thebis(4-hydroxy-6-methyl-s-triazolo[4,3-a]pyrimidine)disulfide wasreplaced by an equivalent quantity of bis(4,6dihydroxy-s-triazolo[4,3-alpyrimidine)disultide. The results weresimilar to those obtained in Example IV.

Example VI The antifogging action ofbis(4-hydroxy-6-methyl-striazol[4,3-a]pyrimidine)disulfide was comparedwith that of 4-hydroxy-6-methyl-3-mercapto-s-triazolo[4,3-a]

It is evident from this table that the bis(triazolopyrimidine)disulfidereduces the fog without loss of speed to a greater extent than mercaptotriazolo pyrimidine which, in addition to its poorer antifoggingperformance, causes serious loss of speed.

Example .VIl

Exposed samples of a photographic film were developed for twelve minutesat C. in a standard metol-hydroquinone developer. Two tests were made,one with the normal developing solution and one with a developercontaining 20 mgs. of bis(4-hydroxy-6-methyl-s-triazolo[4,3-a]pyrimidine)disulfide per liter of developer. Sensitometricstrips, developed in the normal developer (control) for twelve minutes,showed a fog of .28 whereas those strips which were developed in thedeveloper containing the antifoggant had a fog of .20.

Various modifications of the invention will occur to persons skilled inthe art. Thus, it is understood that in lieu of using the particularantifoggants of the examples, any of the antifoggants listed in theapplication may be employed with equivalent results. I, therefore, donot intend to be limited in the patent granted except as necessitated bythe prior art and the appended claims.

I claim:

1. A light sensitive photographic material comprising a base and a lightsensitive silver halide emulsion, said light sensitive materialcontaining as an antifoggant a compound selected from the groupconsisting of those having the following formulae:

wherein R is a member selected from the class consisting of hydrogen,alkyl, alicyclic, aryl, pyridyl and furyl groups, R; is a memberselected from the class consisting of amino, hydroxy, carbalkoxy, alkyl,alicyclic, aryl, pyridyl and furyl groups, R, is a member selected fromthe class consisting of hydrogen and carbalkoxy groups, R is a member ofthe class consisting of hydrogen, methyl and phenyl groups, and X is amember selected from the class consisting of amino and hydroxy groups.

2. The article as defined in claim 1 wherein the antifoggant is locatedin the silver halide emulsion.

3. The article as defined in claim 1 wherein the antifoggant is locatedin a layer adjacent to said silver halide emulsion layer.

4. A light sensitive photographic material comprising a base with alight sensitive halide emulsion thereon, said emulsion containing as anantifoggant the compound, bis- (4-hydroxy 6 methyl-s-triazolo[4,3-a]pyrimidine)disulfide.

5. A light sensitive photographic material comprising a base with alight sensitive silver halide emulsion thereon, said emulsion containingas an antifoggant the compound,bis(4-6-dihydroxy-s-triazolo[4,3-alpyrimidine) disulfide.

6. A light sensitive photographic material comprising a base with alight sensitive silver halide emulsion thereon, said emulsion containingas an antifoggant the compound, bis(4 amino 6 methyl-s-triazolo[4,3-alpyrimidine) disulfide.

7. The process of minimizing and preventing fog in light sensitivesilver halide materials comprising a base having a light sensitivesilver halide emulsion thereon, which comprises exposing said emulsionto light and developing the same in the presence of an antifoggant and Zstabilizer selected from the class consisting of those having thefollowing formulae: 7

dyl and furyl groups, R is a'member selected from the, class consistingof hydrogen and carbalkoxy groups, R; is a member of the classconsisting of hydrogen, methyl and phenyl groups, and X is a memberselected from the class consisting of amino and hydroxy groups.

8. The process as defined in claim 7 wherein the antifoggant isbis(4-hydroxy-6-methyl-s-triazolo[4,3-alpyrimidine)-disulfide.

9. The process as defined in claim 7 wherein the antifogg'ant i'sbis(4,6-dihydroXy-s-triazolo[4,3-a]pyrimdine)- 10. The process asdefined in claim 7 wherein the antifoggant isbis(4-amino-6-methyl-s-triazolo[4,3-a]pyrimdine)-disulfide'.

- References Cited in the file of this patent UNITED STATES PATENTS2,440,110 Mueller Apr. 20, 1948 2,465,149 Dersch et al Mar. 22, 19492,852,375 Tinker Sept. 16, 1958 UNITED STATES PATENT OFFIQE Patent No. 2935 4LO4L Fritz H0 Dersoh May 3 i960 It is hereby certified that errorappears in the printed specification of the above numbered patentrequiring correction and that the said Letters Patent should read ascorrected below.

Column 1,

formula should appear as shown patent:

HO====C Signed and sealed this 18th day of April 1961o (SEAL) Attest:

ERNEST Wt. SWIDER Attest'ing Officer DAVID L. LADD flommissioner ofPatents

1. A LIGHT SENSITIVE PHOTOGRAPHIC MATERIAL COMPRISING A BASE AND A LIGHTSENSITIVE SILVER HALIDE EMULSION, SAID LIGHT SENSITIVE MATERIALCONTAINING AS AN ANTIFOGGANT A COMPOUND SELECTED FROM THE GROUPCONSISTING OF THOSE HAVING THE FOLLOWING FORMULAE: